Variables and Data Types

• Data (information we're going to store)– Numbers– Text– Dates

• What types of data can JavaScript process?• How do we store it?• How do we use it in code?

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Data Types

• Common: Dates, Text, Numbers• Other, more abstract, data types– boolean, etc.

• Strongly typed vs. weakly typed– JavaScript is weakly typed– Java is strongly typed

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Numerical Data

• Integers - range from -2E53 to 2E53• Floating-point numbers (have a decimal place)• JavaScript treats these different when storing

them• JavaScript processes everything as if it were a

floating point• Hides the details from us

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Text Data

• Another term for one or more characters is a String

• JavaScript recognizes strings (as different from code) because they are enclosed in quotes

• You may use single or double quotes– must end with what you started with– e.g. "Steve" or 'Steve', not "Steve'

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Handling Quotes in the Text

• How do you enclose a quote in the text– "Peter O'Toole" or– 'Peter O\'Toole'

• The backslash is an escape character– tells the compiler to treat the next character as

text– or to do something special (e.g. advance to a

newline)

Demo – Handling Quotes

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Pause this slide and click the link below for a…

video demonstration

Exercise

• Write a JavaScript program to display the following exact message (with the double-quotes)

"Hey!", John said, "Don't do that!"

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Special Characters

• \xNN– NN is a hexadecimal number which identifies a

character in the Latin-1 character set– huh?– see Appx. D for translation of characters– e.g. "\x9 Paul Wilton" will print as: (c) Paul Wilton

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Boolean

• A variable that can have a value of true or false is declared as a boolean.

• Example…boolean didItWork;diditWork = true;

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Variables - Storing Data

• Data stored permanently or temporarily• Permanent data is stored in a file or database• Temporary data is stored in a variable– variable values are lost when the page is left– held in computers memory (RAM)

• Example: Storing bank account information vs. loan payoff information

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Variable Naming

• Rules for Naming:– case sensitive– can't use reserved words (see Appx. B)– can't use certain special characters• Example: &, % (see Appx. B)

– can use numbers, but not as the first character

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Question

• Which of these names is a valid variable name?– with– myVariable99– my%Variable– my_Variable– my_Variable&Helper

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Answer

– with (no, reserved word)– myVariable99 (yes)– my%Variable (no, special character)– my_Variable (yes, underscore _ is allowed)– my_Variable&Helper (no, & not allowed)

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I Declare!

• You should declare the existence of a variable by using the "var" keyword

• e.g. var myFirstVariable;• Once declared, a variable can be store any

type of data (weakly typed)

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Assigning Values

• Use the equals ( = ) sign• e.g. myFirstVariable = 101;

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Garbage Collection

• The process of freeing up computer memory that was used to store variables is call "Garbage Collection"

• JavaScript does this automatically• What would happen if it didn't?

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Assigning Variables to Variables

• var myVariable;var myOtherVariable;myOtherVariable = 22;

myVariable = myOtherVariable;

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Basic String Operations

• Concatenation – appending one string to another– var concatString = "Hello " + "Paul";– Spaces are significant

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Mixing Numbers and Strings

• You can freely concatenate numbers and strings (the numbers are converted to strings automatically)

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Exercise

• Code a JavaScript program that declares a variable that holds an age (in years) and a variable that holds a person's name and stores them in a variable in the following format…

Hey Steve, you are 54 years old

• Display this message in an alert box

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Data Type Conversion

• You may need to convert data from one type to another– String to integer [ parseInt( ) ]– String to floating points [ parseFloat( ) ]

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Exercise

• Write a JavaScript program that prompts a user for their age

• Now substract 10 from the user's answer• And display a message in the following

format…

Are you really only 44 years old?

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Data that Won't Convert

• var myString = "I'm a name not a number!";• Returns NaN– Special Value– means Not a Number

• isNaN( ) function– e.g. myVar1 = isNaN("Hello");• TRUE

– myVar2 = isNaN(34)• FALSE

Null Values

• var nullString = null;• var undefString;

• var blankString = ""; //has a value of empty string

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End of Lesson

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